A known method for directly controlling a hydraulic pressure that is applied to a friction engaging element from a hydraulic pressure source by means of an electromagnetic valve without an accumulator has been disclosed. To realize a smooth and high-response transmission feeling, it is important to obtain a hydraulic pressure characteristic value used for the hydraulic pressure control (piston stroke control) which is applied to the friction engaging element. In US2003-0216218A1, which is filed by a applicant of the present invention, a learning method is disclosed, wherein a pre-charge maximum time and a stand-by pressure are set as the hydraulic pressure characteristic values in accordance with variation in a turbine rotation number Nt. The pre-charge maximum time is used in an initial stage when the hydraulic oil is rapidly applied to the friction engaging element, and the stand-by pressure is used for maintaining the friction engaging element at a position right before its engagement. According to the known method, entire individual differences, which will occur in an initial stage of the shipment, can be eliminated, and then the hydraulic pressure characteristic value can be set and learned by a service staff of a car dealer even when the automatic transmission whose hydraulic pressure characteristic value can be set has been shipped.
If the hydraulic pressure characteristic value will be set and learned by the service staff (operator) of the car dealer, operational behavior of the operator needs to be considered. For example, during the learning control, if the accelerator is pressed or released by little and little when the vehicle is in an idling state, an accurate learning result may not be obtained.
Further, the learning control is required after an engine rotation number is increased by pressing down the accelerator so as to stabilize the engine rotation number, an accurate learning result may not be obtained due to differences of the operational behavior of the operator. For example, if the operator sees an instruction saying “press down on the accelerator so as to stabilize as possible”, the level of the pressing may vary from person to person, as a result, the learning result may vary. In the same manner, the operator may release the accelerator before the engine rotation number has not stabilized for a predetermined time period. Such problem may be solved if instructions have made in detail, however it is considered that more stabilized result can be obtained if the differences depending on the operator's behavior can be eliminated by controlling on the automatic transmission side.
Thus, a need exist for an hydraulic pressure characteristic value to eliminate not only differences depending on each automatic transmission unit but also differences depending on the operator's behavior.
Another known method for directly controlling a hydraulic pressure that is applied from a hydraulic pressure source by means of an electromagnetic valve without an accumulator to a friction engaging element (a friction clutch or a friction brake) so as to be engaged or disengaged is disclosed.
In the process for controlling a hydraulic pressure applied to the friction engaging element of the automatic transmission, a pre-charge operation is executed during a first stage of a piston stroke by increasing the amount of the hydraulic oil so as to be rapidly applied to the friction engaging element. And then, the amount of the hydraulic oil is reduced so as to maintain the friction engaging element at a low hydraulic pressure (stand-by pressure) that corresponds to a pressure of a return spring for a predetermined time period so as to prevent a surge pressure upon a stroke end.
Further, the hydraulic pressure control characteristic during the pre-charge process may vary depending on individual differences of the automatic transmission or the engine. According to the know method, the individual differences, which will occur in an initial stage the shipment, can be eliminated. Specifically, a guard method for disengaging the friction engaging element when a variation range of the turbine rotation number reaches a predetermined guard rotation number is provided in the know method. More specifically, the guard method can avoid damage on the friction engaging element because of the friction engaging element slides for a long time period when the hydraulic pressure characteristic value has not determined during the hydraulic pressure characteristic value setting, or avoid mechanical damage on the friction engaging element because of an excessive torque applied for a long time period to the friction element in the pre-charge process US2003-0216218A1 .
For automating the manual transmission (MT), a torque point learning method is disclosed in U.S. Pat. No. 6,658,341B2. In the torque point learning method, a torque point of a multi-plate wet clutch that is provided between the torque converter and the MT, can be learned by the drover. In this method, the engaged clutch is disengaged when one of the following conditions is fulfilled so as to prevent MT from being malfunctioning or mechanical damaging. (1) A difference (N) between the engine rotation number (Ne) and the turbine rotation number (Nt) becomes equal to or more than a predetermined number (e.g.N300 rpm), or the difference (N) between the engine rotation number (Ne) and the turbine rotation number (Nt) becomes equal to a engine rotational difference ( Ne50 rpm)This condition includes the torque point condition. (2) The vehicle starts traveling (speed≠0 km/h). This condition presumes a case when some kind of problem has occurred on MT.
(3) Knob switches on the first, third and fifth speed are turned on. In this condition, it is determined that the drive made a miss operation. (4) The engine rotation number becomes away from the engine rotation number upon the idling state (Ne300 rpm or 80 rpm). This condition presumes a case when some kind of problem has occurred on MT. (5) The parking brake is released. In this condition, it is determined that the drive made a miss operation. (6) The foot grace is released. In this condition, it is determined that the drive made a miss operation.
However, the known guard method during the hydraulic pressure characteristic value setting (learning) is a minimum guard in consideration with a safety matter, and in may happen when the hydraulic pressure characteristic value is learned after the vehicle is shipped that the setting process can not be finished because the hydraulic pressure characteristic value has not been determined. Further, there is a need to improve safety of the guard method to prevent the automatic transmission or MT from being malfunctioned or mechanical damaged.
Thus, a need exists for a guard method and a control device for executing the guard method, which are executed in the hydraulic pressure characteristic value setting, to prevent the automatic transmission from being malfunctioned or mechanical damaged.
Further, another need exists for a guard method and a control device for executing the guard method, which are executed in the hydraulic pressure characteristic value setting, to notice promptly that the determination in the hydraulic pressure characteristic value setting (learning).
Still another known method for directly controlling a hydraulic pressure that is applied to a friction engaging element from a hydraulic pressure source by means of an electromagnetic valve without an accumulator has been disclosed. To realize a smooth and high-response transmission feeling, obtaining a hydraulic pressure characteristic value used for the hydraulic pressure control (piston stroke control) which is applied to the friction engaging element is important.
In this circumstance, a method for learning the hydraulic pressure characteristic value by directly detecting a position of the clutch piston, a method for learning the hydraulic pressure characteristic value by directly detecting the hydraulic pressure and a method for learning the hydraulic pressure characteristic value by directly detecting the torque, have been proposed. It is well known that a value of the clutch stroke can be detected on a dry-type friction clutch, however according to a wet-type friction clutch, the stroke amount of the clutch piston is small (e.g. 2 mm), so that the accuracy on the stroke sensor needs to be improved for directly detecting the position of the clutch piston. If the stroke sensor is improved, the cost of the automatic transmission is increased. Further, such stroke sensor may be applied to the brake, however application to the clutch is practically difficult.
The applicant of the present invention disclosed a method for executing the learning the hydraulic pressure characteristic value in accordance with variation in the turbine rotation number Nt in US2003-0216218A1. This method, in which the hydraulic pressure characteristic value is determined in accordance with variation in the turbine rotation number, has many advantages comparing to the above methods. The applicant also disclosed a method for executing the learning for the pre-charge maximum time, which is used when the hydraulic oil is rapidly applied to the friction engaging element during an initial period of the hydraulic pressure application process, and for the stand-by pressure, which is used for maintaining the friction engaging element at a position right before it moves to be engaged.
In the learning of the stand-by pressure, an accurate return spring corresponding pressure can be obtained by driving the clutch piston so as to increase in an stepped hydraulic wave form, in which a step pressure is small with enough intervals. The variation in the turbine rotation number is very slow, so that a threshold of the variation in the turbine rotation number needs to be reduced to prevent the determination from being delayed, however, the sensor for detecting the turbine rotation number has a limitation. There is no problem if all the friction engaging elements has allowance to the threshold, however, allowance may differ depending on each of the friction engaging element, and some friction engaging element, whose relative rotation number is small, and torque division ration relative to the input torque is small, has little allowance to the threshold.
In addition, the deceleration of the turbine rotation number may further be gentle due to an actuation of the accumulator, leaking from a seal portion (e.g. damage on an O-ring), a slow actuation on a control valve (stuck) or the smaller actual pressure than a indicated pressure, and the determination on the stand-by pressure may delays.
To prevent the delay of the determination, a predetermined standard may be provided so as to eliminate the value if the is out of the standard (not using the leaned value), however, according to the method disclosed by the applicant of the present invention, even when the process has passed a point, at which the determination should have made, the pressure is applied to the friction engaging element, so that the deceleration of the turbine rotation number is increased, as a result, the value always enters the standard range. Even when the value is in the standard range, the value exceeds the true value, which result in an engagement to the end upon an actual transmission.
Similar problems has been seen when the hydraulic pressure variation happens while the learning of the pre-charge maximum time. In the pre-charge maximum time learning, the clutch piston is controlled so as to be engaged with the friction engaging element at a cracking speed. Thus, the deceleration on the turbine rotation number becomes large, and the determination is not diverse.
Further, if the hydraulic pressure variation varies, the pre-charge maximum time extends more or less, and the determination has been finished properly, so that it cannot be distinguished whether or not hydraulic pressure variation happens. In most cases, a difference on the pre-charge maximum time, which is occurred depending on whether or not the hydraulic pressure variation exist is small, and the learning value when the hydraulic pressure variation occurs enters within the production standard. If the hydraulic pressure variation is identical with a hydraulic pressure variation occurred in an actual transmission, a transmission shock can be comprehend due to the hydraulic pressure variation. However, if the hydraulic pressure variation is not identical with a hydraulic pressure variation occurred in an actual transmission, a end engagement may happens, which result in a transmission shock.
Specifically, without damage on the learning of the stand-by pressure and pre-charge maximum time, it will be preferable if a measure for the learning value, which is large within a product standard, relative to a true value is considered. Thus, a need exists for a setting method for a hydraulic pressure characteristic value setting to improve the know method disclosed in US2003-0216218A1.